Welding in carbon steels with standard solid wire in protected atmosphere. Welding in inner angle These wires are welding in opposite polarity to the rest of the MIG-MAG welding. In this case the polarity of the gun is negative and the mass is positive, and the slag is eliminated as if it were an electrode. Welding at structural level in outdoor applications. We work with negative polarity in the gun and positive mass unlike the traditional mig-mag systems. Ascending vertical welding, gun polarity is negative and the mass is positive.